Why are some children born with congenital heart defects?

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Dr. Mark S. Sklansky, MD
Pediatric Cardiologist

We are continuing to learn more about the causation/etiology of congenital heart defects. But still, the vast majority of the time, we cannot pinpoint the exact cause for any given child’s congenital heart defect. In a minority of cases, specific causes can be identified, and may include the presence of a genetic syndrome with a well-established genotype (such as Down syndrome), a history of being exposed to a known cardiac/heart teratogen before birth or a history of being born to a mother with diabetes, systemic lupus erythematosus (SLE) or other chronic diseases that have been established to be associated with the formation of congenital heart defects in children. Determining the cause of an individual child’s congenital heart defect may have important implications on prognosis, and may provide insight into the likelihood of recurrent heart disease in subsequent generations.

Dr. Coleen Boyle, PhD, MS
Public Health & General Preventive Medicine Specialist

The cause of most congenital heart defects is unknown. Some babies have heart defects because of changes in their genes or chromosomes. They also might be caused by a mix of genes and other risk factors. The Centers for Disease Control and Prevention's (CDC) National Birth Defects Prevention Study (NBDPS) has found that women who are obese, have diabetes, or smoke during pregnancy increase their chances of having a baby born with a heart defect.

The presence of the CDC logo and CDC content on this page should not be construed to imply endorsement by the US Government of any commercial products or services, or to replace the advice of a medical professional. The mark “CDC” is licensed under authority of the PHS.

Most of the known causes of congenital heart defects are due to occasional genetic changes, but large chromosomal alterations are also commonly involved, such as those that cause Down syndrome. Since the development of the heart is the consequence of an exact sequence of events early in pregnancy, there are many opportunities for mutations to cause defects. In addition, factors such as maternal infection, illness, medications and drug use are all associated with congenital heart deformities.

Dr. Deborah Raines, MSN
Nursing Specialist

A congenital heart defect is an abnormality or malformation in any part of the heart that is present at birth. Heart defects originate in the early weeks of pregnancy when the heart is forming. The human heart begins as a single tubular structure during the fourth week of pregnancy. By the eighth week, this tube has increase in length. It twists upon itself and a wall, or septum, grows to divide the upper (atrial) and lower (ventricular) chambers into left and right sides. Four valves made of tissue develop, which keep blood moving forward through the cardiac chambers, lungs, and body as the heart pumps. Multiple environmental and genetic factors influence development of body organs during this first trimester of pregnancy. Some potential causes of congenital heart defects include:

  • Exposure to certain drugs/pharmacotherapeutic agents, industrial chemicals, during the first trimester
  • Uncontrolled diabetes
  • Chromosomal abnormalities
  • Maternal viral infection during the first trimester of pregnancy
  • Presence of a congenital heart disease in a parent or sibling

However, the cause of many congenital heart defects remains unknown. Yet, heart defects are among the most common birth defects.

Much is still unknown about the causes of congenital heart disease, and in most cases a cause is never identified. Some heart defects have a genetic link, while others may be influenced by environmental factors—or some combination of genetic and environmental. The following non-genetic risk factors have been found to contribute to varying degrees to congenital heart disease:

  • Maternal smoking during pregnancy
  • Maternal obesity
  • Exposure to certain air pollutants, solvents, and pesticides
  • Low levels of maternal folic acid ingestion during pregnancy
  • Poorly controlled pre-pregnancy and gestational maternal diabetes

Congenital heart disease, or congenital heart defect, is a problem with your heart that is already there when you are born. Scientists are not sure of the actual cause, but they believe that a number of factors can contribute to its development:

  • Genetics. Often if one child has congenital heart disease, their siblings will have it as well.
  • Other medical conditions. If you have had rubella (German measles) or diabetes during pregnancy, your baby may be at risk for congenital heart diseases.
  • Smoking during pregnancy.
  • Certain medications.

Scientists continue to study congenital heart disease in the hopes that they will one day find the cause.

Many parents feel responsible after finding out their child has a heart defect. In this video, cardiothoracic surgeon Dr. Emile Bacha explains why moms and dads aren't to blame for congenital heart defects.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.